Abstract
Utilization of untreated urea (F0) and urea treated with 1.5 % formaldehyde(F1.5) was tested in vitro on incubation substrates with different levels of crude protein: 9, 10, 11, 12, 13, 14, 15 and 16 % of the substrate dry matter. The content of crude protein was adjusted by addition of urea, the lowest level (9 %) being that of the substrate without urea. The incubation time was five hours. When F0 urea was used microbial protein synthesis, determined by tungstic acid-sulphuric acid precipitation, reached its maximum at the crude protein level of 11 %. When F1.5 urea was added, the synthesis increased up to the level of 15 % crude protein. At the levels of 13-15% crude protein, the synthesis was significantly (P< 0.05) higher with F1.5 urea than with F0 urea. In the bacterial mass obtained by ultracentrifugation the content of methionine was significantly higher (P< 0.01) when treated urea was used. With untreated urea, the proportion of lysine was significantly higher (P< 0.05). Addition of urea did not affect the amino acid composition of the bacterial mass but increased the yield of microbial protein during incubation.
Highlights
In many of the papers reviewed by MOLLER (1979) rumen ammonia concentration has been shown to be a critical factor for ammonia utilization in the rumen, when the basal ration is supplemented with urea
With the treated urea (F, 5 ) protein synthesis was lower than with the untreated urea up to the level of 13 % crude protein. After this level microbial protein synthesis increased in the F] 5 incubations and the peak of synthesis was not reached until the level of urea 15 % crude protein
If the ammonia levels are calculated according to the results obtained earlier (SETÄLÄ and SYRJÄLÄ-QVIST 1982) for the feed substrate alone and for both kinds of urea, the optimum ammonia concentration was 10-11 mmol NH3/1, which is higher than those suggested elsewhere, for instance in the review by MÖLLER
Summary
In many of the papers reviewed by MOLLER (1979) rumen ammonia concentration has been shown to be a critical factor for ammonia utilization in the rumen, when the basal ration is supplemented with urea. The critical crude protein level can vary considerably, depending on such factors as the solubility and degradability of the nitrogen in the basal ration (AITCHISON et al 1976, ROY et al 1977) and the content and quality of energy in the ration (MOLLER 1973, SATTER and ROFFLER 1976, KROPP et al 1977). The object of this experiment was to study how urea utilization is affected by the rate of urea degradation on diets with different levels of crude protein and a constant energy content
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